1. Field of Invention
The present invention relates to a back light module, and more particularly to a light mixing apparatus applicable to a back light module.
2. Description of Related Art
With the benefit of advance of development in manufacturing semiconductor elements or display devices, the multimedia technology at present reaches a very high level. With respect to display devices, liquid crystal displays with the advantages of high picture quality, compactness, low power consumption, free radiation and the like have become a mainstream in the market.
Since the LCD panel itself does not have a light emitting function, a back light module must be disposed under it to provide a planar light source for the LCD panel. As the LED has the advantages of high brightness, low power consumption, long life span, less thermal-dissipated problems and the like, an LED array has been widely used in the back light module nowadays.
FIG. 1 is a schematic sectional view of a conventional back light module, and FIGS. 2A and 2B are a schematic view of the light emitting shape of a side emitting type LED, respectively. Referring to FIGS. 1 and 2A first, the bottom lighting type back light module 110 mostly employs a side emitting type LED 100 shown in FIG. 2A as a light emitting source, and the side emitting type LED 100 can convert a point light source into a plane diffusing light source through lens (not shown) of its own package structure. That is to say, most of the light emitted by the side emitting type LED 100 is converged in the region A1 on both sides.
In the back light module 110, a diffusion plate 120 is disposed above the array formed by side emitting type LEDs 100. When the back light module 110 is lit, the light emitted by the side emitting type LEDs 100 at different positions will be sent out through the diffusion plate 120 after being mixed, thereby forming a planar light source with uniform brightness.
It should be noticed that if the distance between the diffusion plate 120 and the side emitting type LEDs 100 is much small, the light provided by the back light module may not be mixed uniformly. To provide enough distance for mixing the light emitted by the side emitting type LEDs 100, the current implemented method is to enlarge the distance between the diffusion plate and the side emitting type LEDs 100. However, this method will increase the overall thickness of the back light module, which is contradictory to the light-and-thin design trend of the back light module.
Referring to FIGS. 1 and 2B, in the back light module 110, colors are most likely to be mixed non-uniformly at an edge of the array formed by side emitting type LEDs 100. As the red side emitting type LED 100R, blue side emitting type LED 100B and green side emitting type LED 100G are separated from each other by a pitch respectively, the illumination range of each side emitting type LED (100R, 100G and 100B) is limited, and only the light emitted by the green side emitting type LED 100G adjacent to the edge can reach the region A2, thus causing a non-uniformly-mixed light in the region A2 and accordingly the occurrence of an apparent single-color (green) cast phenomenon. Therefore, the conventional back light module 110 cannot provide the uniformly mixed light, thereby deteriorating the display quality of LCDs.